Devices, known as "tensioning" switching magnets, serve as security devices which facilitate manual engagement when, for example, during breakdown of the magnetic field excitation or during a mechanical blockade despite magnetic field excitation, no movement of the armature occurs counter to the effective spring force. The ability to manually move the armature in such events is particularly advantageous, especially when the relevant switching magnet serves in hydraulic installations for the actuation of a multi-way valve for the control of the pressure oil supply, for instance, for use in a press or in a working cylinder. In such environments, it is essential to avoid danger, so that in emergency situations the pressure oil supply can be retained manually.
Known devices of this type, as disclosed in DE 33 17 226 A1, have complicated constructions and have relatively great numbers of individual component parts. Another drawback resides in that because of the great number of individual parts and because of the conditions under which the pole pipe must be mounted with construction of devices on both sides, a higher cost of assembly occurs.